This invention relates to novel soft contact lenses and a novel process for making said soft contact lenses.
It is well known that contact lenses are becoming more and more popular, since they have many advantages over the conventional spectacles. For example, contact lenses are very light, are convenient for wearers in action and movement, are desirable from the viewpoint of personal appearance, and offer eyesight correction over a remarkably broad visual field. Contact lenses have conventionally been made of plastic materials. However, the prior art contact lenses are made of materials mainly comprising methyl methacrylate polymers and thus they are hard. Hence, they often fit poorly over the cornea, cannot be worn for a prolonged period of time, and frequently fail in adaptation causing lacrimation, a feeling of foreign matter, a feeling of dryness and the like. Moreover, polymers of methyl methacrylate do not have sufficient impact resistance, and lenses of these materials are easily broken and are likely to injure the eyes. So, they are not satisfactory from the viewpoint of safety.
Recently, with a view to overcoming these defects of the prior art hard contact lenses, soft contact lenses have been developed, which have far better affinity to the cornea and which give less feeling of foreign matter and/or dryness. Opticians and ophthalmologists have much interest in these soft contact lenses as the means not only for eyesight correction, but also for compensation of aphakia after a cataract operation, as lenses to be used for treatment of eye diseases or to be worn after the treatment of trauma of eyes.
However, the soft contact lenses that have hitherto been developed have very serious defects in quality and are difficult to manufacture, which prevent them from general acceptance. The presently known soft contact lenses are made of hydrophilic polymers, mainly comprising poly(hydroxyethyl methacrylate). These materials absorb water and swell until the equilibrium is attained, and in the wet and swollen state they are soft and flexible. Therefore, the known soft contact lenses are characterized in that they are always used in the swollen state. In such a swollen state, however, high molecular materials generally are markedly reduced in mechanical strength and are extremely fragile. In addition, since they are worn always in the wet and swollen state, these soft contact lenses are easily contaminated with bacteria. Therefore, they need to be sterilized once a day by boiling. This boiling treatment is not only troublesome but often causes decomposition and breakdown of the lens material. Thus the prior art soft contact lenses are very short-lived because of their characteristics of being used in the wet and swollen state. This is a serious practical defect and prevents their wide acceptance.
Also, the prior art soft contact lenses are difficult to manufacture. Although the prior art soft contact lenses are used in the swollen state, the work of shaping and finishing, such as cutting, machining, polishing, etc. must be applied to the polymeric material in the dry state, but it is very difficult to tell beforehand the precise shape, size, curvature and the like which the lense will assume in the swollen state. Also, even a slight variation in the atmosphere or conditions under which polymerization is carried out may results in variation in hydrophilic property and swellability of the product, which makes the quality control extremely difficult. In short, the known process for manufacturing the prior art soft contact lenses is complicated and difficult to control and percentage of rejection is very high.
We have searched for new materials suitable for soft contact lenses and for a manufacturing processes therefor that will not result in the above-mentioned defects in quality and disadvantages in manufacturing, and we have completed this invention.